The present invention relates to a liquid injection apparatus, in particular to a liquid injection apparatus for use in a method of lining the internal surface of an existing pipe buried under ground.
There has been known a no-excavation underground pipe lining method in which the internal surface of an existing underground gas pipe, water pipe, etc. are lined with a resin without the necessity of any trenching or excavation. For example, a gas service pipe is buried underground branching from a gas main and extending to a user's house. In the method called no-excavation underground pipe lining, there are substantially two steps involved. In the first step, a pressurized liquid is used to produce a pushing force to introduce a necessary amount of resin into the service pipe through an open end thereof and to move the resin through the pipe until the front end of the resin plug flow reaches an inner end (a position branching from a gas main) of the pipe. In the second step, a suction force is used to suck the resin back from the inner end so as to line the internal surface of the pipe with the resin.
A series of equipments for producing the pressurized liquid and for injecting the same into a gas service pipe, include a liquid tank, a liquid pump and a liquid injection controlling device, all of which are successively connected in series to the open end of a gas service pipe.
However, since the liquid tank, the liquid pump and the liquid injection controlling device must be individually disposed on the ground near the open end of a gas service pipe, and connected in series by several hoses to the pipe, a relatively large ground space is required. Also, since the liquid tank, the liquid pump and the liquid injection controlling device are transported and arranged on the ground in a separate or spaced relationship with one another, the transportation and arrangement thereof have been considered inconvenient.
Moreover, although the liquid injection controlling device is useful for controlling the pressure of the liquid being supplied from the liquid tank and stopping the liquid injection when a predetermined amount of liquid has been injected into the pipe, it fails to cope with pressure changes in the liquid which has already been injected in the pipe and is flowing therethrough. Such pressure changes are usually caused due to a larger or smaller diameter portion involved in a gas service pipe.
Namely, a gas service pipe may involve one or more irregular portions whose diameters are larger or smaller than that of the service pipe itself. If one or more such irregular portions have a diameter larger than the pipe diameter, a predetermined amount of liquid which is usually calculated only in accordance with pipe diameter and pipe length, will be insufficient for moving the injected resin to an inner end of the service pipe, resulting an incompleted lining treatment. Another problem associated therewith is that the lining resin and lining pig(s) will drop into the larger diameter portion, rendering it impossible to continue the lining treatment any further and later suck back the dropped resin and pig(s). On the other hand, if one or more irregular portions have a diameter smaller than the pipe diameter, a predetermined amount of liquid will be too much for moving the injected resin to the inner end of the pipe. As a result, a part of the resin will move past the inner end (a position branching from a gas main) and drop into the gas main. Another problem associated therewith is that lining pig(s) will get stuck and become unmovable in a smaller diameter portion, rendering it impossible to continue the lining treatment any further and later suck back the dropped resin and pig(s).